INDIANAPOLIS (AP) — Andrew Luck watched one last game from the sideline Saturday.

Then he said goodbye to the NFL.

The Indianapolis Colts quarterback heard boos as he walked away from the field, then walked to the podium and made the surprise decision official: The oft-injured star is retiring at age 29.

"I'm in pain, I'm still in pain. It's been four years of this pain, rehab cycle," Luck said. "It's a myriad of issues — calf strain, posterior ankle impingement, high ankle sprain. Part of my journey going forward will be figuring out how to feel better."

Luck wasn't planning to make the announcement following Saturday's 27-17 loss to the Chicago Bears. But when ESPN first reported the news during the fourth quarter, Luck changed the plan for a Sunday afternoon announcement.

Instead, he held a 25-minute impromptu news conference.

At times he sounded wistful. At others, his voice cracked with emotion.

One thing was clear: The endless barrage of injuries stripped away his joy for the game and prompted him to walk away so he could enjoy the life he wants.

"There's no doubt when you hear him talk about the cycle of pain and injury and rehab, you can hear that," coach Frank Reich said. "There's a saying in football that everyone knows and everybody lives by, it's next man up and even though this situation is unique, no one is exempt."

That task now falls to Jacoby Brissett, a fourth-year player whom the Colts acquired in a cutdown weekend trade two years ago who has been practicing with the starters since April.

He went 4-11 as a starter in the 2017 season after taking over for opening day starter Scott Tolzien.

But the Colts had already been preparing for the possibility Luck might not be ready for the Sept. 8 season opener against the Los Angeles Chargers. Luck was diagnosed with a strained left calf in March and team officials kept him out of all of the team's offseason workouts.

He returned to limited action when training camp opened in late July. After three practices, though, the lingering pain near his ankle forced him back into rehab. He hadn't practiced with the team since, though he did throw passes in pregame warmups before last week's preseason game.

"I had a thought that it might be my last time throwing at Lucas Oil as a current member of the Colts team," Luck said. "And I wanted to make sure I could go out and enjoy it."

It wasn't just the leg, though.

He played with shoulder pain for most of 2015 and 2016, and his 2015 season ended when he suffered a lacerated kidney. He missed all of 2017 following shoulder surgery and then the happy-go-lucky former Stanford star dealt with more pain and more endless months of rehab.

The Colts bet big on Luck in 2012.

They cut an injured Peyton Manning to take Luck with the top overall pick, fully believing he would be their franchise quarterback for the next 10 to 15 years.

Team owner Jim Irsay called it a "no-brainer" because his aging team needed to rebuild.

"I never felt that he (Luck) owed me to play until he's 40 or until he's 36 or whatever," Irsay said. "I mean, this is an unusual situation."

Luck delivered quickly on his promise.

He led the Colts to the playoffs in each of his first three seasons and to the AFC championship game after the 2014 season — without missing a start. But a subpar offensive line struggled to keep Luck upright and in 2015, the shoulder and kidney injuries forced him to miss nine games. The Colts finished 8-8 and missed the playoffs.

In 2016, after Luck opted not to have shoulder surgery, then coach Chuck Pagano gave Luck extra days off to try and keep him healthy. Luck made 15 starts that season though the Colts again finished 8-8 and missed the playoffs.

While Luck had surgery for a partially torn labrum in January 2017, he never felt right and after throwing for two weeks in the fall was shut down for the rest of the season.

Last year, Luck looked like his old self. He established career highs in attempts (639), completions (430) and completion rate (67.3 percent), throwing for 4,593 yards with 39 touchdowns and 15 interceptions as he led the Colts back to the playoffs, earned his fourth Pro Bowl selection and was the runaway winner of the league's Comeback Player of the Year award.

Then came the mysterious calf-ankle injury that again never felt quite right.

So after marrying his longtime girlfriend this spring and now awaiting the birth of his first child, Luck called it quits.

"I am going to retire," he said. "This is not an easy decision. It's the hardest decision of my life. But it is the right decision for me."

Players around the league were just as stunned as the Colts.

"It was mind-blowing," Houston Texans quarterback Deshaun Watson said. "It's something that of course caught everyone off guard. He can control his own future. He's a great player. He's a great quarterback. One of the top five quarterbacks in the league. He's doing it for the right reasons for himself."

Kansas City quarterback Patrick Mahomes, the reigning MVP, said: "Knowing Andrew he's a great football player, of course, but he's also a great human being — I know that he's going to make the right decision for himself and his family."

Seattle quarterback Russell Wilson, who was in the same draft class as Luck, said he found out from offensive tackle Duane Brown before the Seahawks' game against the Los Angeles Chargers and was surprised, like everyone else.

"We all expect we're going to play this game forever. The reality is for most players, it's not very long," Wilson said. "I've always loved being around him, and the times we've gotten to be around each other. I know this has to be really hard on him. Just praying for him to stay encouraged."

Reich had said he hoped to have an answer about Luck's availability for the Sept. 8 season opener after the third preseason game. This might not have been the one he wanted — and certainly didn't expect.

"Teams win, don't write the end of the story yet," Colts general manager Chris Ballard said. "I'm telling you the story's not over yet."

Luck finishes his seven-year career with 2,000 completions, 3,290 attempts, 23,671 yards, 171 touchdowns and 83 interceptions and those stinging boos as he left the field.

"I'd be lying if I said I didn't hear the reaction," he said. "It hurt, I'll be honest with you, it hurt."

BEARS DEFENSE

Chuck Pagano, Luck's first coach, returned to Lucas Oil Stadium for the first time since his firing shortly after the 2017 season.

The new Bears defensive coordinator made a splash.

Despite both teams sitting all of their starters including Brissett, the Bears used their second defensive touchdown to take the lead for good late in the third quarter.

Trailing 10-0 early in the second quarter, safety Deon Bush ripped the ball out of the air from rookie tight end Hale Hentges got up and scored on a 91-yard interception return. After two field goals from Eddy Pineiro made it 17-13, linebacker Joel Iyiegbuniwe returned a fumble 22 yards to give the Bears a 20-17 lead.

Chicago closed out the scoring with a 17-yard TD pass from Tyler Bray to Jesper Horsted.

Bray was 11 of 16 with 136 yards and Ryan Nall had two carries for 73 yards.

Chad Kelly led the Colts to all three of their scores and was 16 of 21 with 209 yards and one touchdown — all in the first half. Deon Cain caught three passes for 74 yards, including a 46-yard TD catch.

PINEIRO STICKS IT

The Bears spent the whole offseason looking for a kicker. And it looks as if they found the right one.

Less than a week after giving Pineiro the job, he made all three of his field goals, including a 58-yarder in the third quarter. His previous long during the preseason was 41 yards.